Milling machines, commonly used by operators for milling items, such as metal, plastic or wood are available in various forms and from various manufacturers. The majority of milling machines include a head assembly which includes a spindle and a quill. The spindle holds a milling tool used for milling a workpiece and the head assembly includes a spindle motor for causing the spindle to rotate within the quill. The quill and spindle is typically movable along a third axis of movement which is perpendicular to the first and second axes of movement, such third axis generally defined by a vertical line extending in both directions through the center of the spindle. Milling machines are generally operated in substantially three modes: manual operation; and computer controlled or aided two axis operation and computer controlled or aided three axis operation. In manual operation, a milling machine operator manually turns x or y cranks to desirably position the workpiece, often tracking the movement via position indicating dials, electronic readouts or other similar means. In this way, a workpiece can be manually moved relative to the rotating spindle within the quill to an appropriate location for desired machining. In two or three axes computerized numerically controlled or aided (CNC) milling machines, programmed positioning is provided along either two or three axes of motion. In two axis computer controlled or aided machine, a computer typically receives position information from an operator or from a stored program and controls the positioning of the machine along the axes of motion to a desired position based on the position information received. Movement of the quill along the third axis, or z-axis, is typically left to be manually operated.
In a three axis machine computer controlled or aided, movement of the quill along the third axis is also automated. Dedicated three axis milling machines are more expensive and are not suitable for the production of one or a few prototype workpieces given the time and effort required to properly program such machines to produce a particular desired workpiece.
In normal operation of a manual or two axis computer controlled or aided milling machine, a workpiece is manipulated into a desired position relative to a tool mounted in a spindle, for example, by an operator turning hand cranks so that the table holding the workpiece moves along x and y axes of movement to a desired position relative to the spindle or by computer controlled or aided. Once adequately positioned, the operator mills or drills the workpiece with the tool by manually rotating an adjustment lever about an axis of rotation adjusting the depth of cut causing the quill to move vertically downward along the z-axis of movement. The tool mounted within the spindle contacts the workpiece as the spindle rotates within the quill.
In prior embodiments of 3 axis computer controlled or aided machines, servo motors have been used to move the quill in the z-axis, such motors substantially interfering with the ability of an operator to manually position the quill along the z-axis.
Other prior inventors have attempted to alleviate this problem by providing various quill control mechanisms, for example, Welch et. al, U.S. Pat. No. 5,330,298 teaches the positioning of controlling elements so that both manual positioning of the quill and automatic positioning of the quill can be achieved. Welch et. al fails to provide, however, a fine feed adjustment mechanism to enable an operator to manually adjust the quill along the z-axis with the precision, speed and efficiency required in commercial operations, for example, the production of one or a few prototype workpieces. Still other prior inventors have conceived of position indicating mechanisms. For example, Vershowske et. al, U.S. Pat. No. 4,909,683 describes a scale adapted to provide a highly accurate digital readout of the linear position of a quill. Vershowske et. al, however, must still rely upon the manual ability of an operator to properly control the existing coarse lever control on existing milling machines in an attempt to achieve the desired vertical movement, regardless of how well the vertical movement is indicated on a positioning mechanism. In other words, reliance upon the existing coarse vertical adjustment mechanisms on existing machines is insufficient to provide repeatable and accurate operation of a milling machine to small tolerances, regardless of the degree of accuracy of the readout provided.
Still other inventors have conceived of stop assemblies for milling machines to provide quick and accurate adjustments of a stop assembly setting (see, for example, Obrecht et. al, U.S. Pat. Nos. 5,252,010; 5,106,242; Ginter, U.S. Pat. No. 4,521,144; Kronfeld, U.S. Pat. No. 4,574,441; Guthrie, U.S. Pat. No. 4,787,794). Others disclose adapters for mounting depth gauges onto milling machines (Escobedo et. al, U.S. Pat. No. 5,286,147). All previously existing milling machines suffer, however, from a particular shortcoming in that none of them provides for a way in which to easily provide a fine feed mechanism in the z-axis which allows an operator to manually gauge depth within 1/10,000th of an inch without the need for complicated and time consuming adjustment of automatic/computer operated controls and still maintain coarse adjustment functions.
Thus, none of the prior art devices is suitable for the production of one or a few number of prototypes in a cost effective and time efficient manner. A long-felt but unsolved need therefore exists for a fine feed adjustment mechanism that is preferably retrofittable to existing machines, that is relatively inexpensive, easy to operate, and that does not interfere with the original operation of the handles provided on existing machines for more coarse adjustment of a quill along the z-axis. The present invention, as described in greater detail below, provides a solution to this long-felt but unsolved need.